It is becoming apparent that in the future battery systems will be used increasingly both in stationary applications and in vehicles such as hybrid and electric vehicles. In order to be able to meet the requirements in respect of voltage and available power which are set for a specific application, a high number of battery cells are connected in series. Since the current provided by such a battery needs to flow through all of the battery cells and a battery cell can only conduct a limited current, often battery cells are additionally connected in parallel in order to increase the maximum current. This can be achieved either by providing a plurality of cell windings within a battery cell housing or by externally interconnecting battery cells.
For reasons of safety and in order to determine the state of charge of the battery with sufficient accuracy, various measured variables such as the voltages of the individual battery cells (cell voltages), the current through the battery and the temperature of selected or all battery cells are usually determined in such battery systems. These measured variables are detected, further-processed and, depending on the application, communicated to other parts of the apparatus by a control unit (battery control unit, BCU).
Since the battery voltage of such a battery system can reach high values, for safety reasons it needs to be constructed so as to be isolated from parts of the surrounding apparatus with which contact can be made. In particular in the case of battery systems which are used in motor vehicles as traction battery, this means that the battery system needs to be implemented so as to be isolated from the control unit because said control unit is connected to the low-voltage power supply system and communicates with other numerous components.
Such isolation or electrical isolation involves increased technical complexity, however, and increases the overall costs of the arrangement. It is therefore desirable to minimize the number of isolation points or electrical isolation points. In accordance with the prior art, depending on a respectively used semiconductor technology or the dielectric strength thereof a cell voltage detection unit which is manufactured using semiconductor technology wholly or partially as a microchip is used for a number of battery cells, for which the sum of the cell voltages does not place excess demands on the dielectric strength of the cell voltage detection unit. The battery cells are then combined with the associated cell voltage detection unit to form a battery module. The individual cell voltage detection units are then interconnected via a communications bus to form a chain, which is connected to the microcontroller, which forms the heart of the control unit, via an individual isolator module. However, there is now the problem that the measurement of the battery current also needs to take place taking into consideration the safety specifications. In this case, magnetic-field-based or voltage-based methods for current measurement can be used. The magnetic-field-based current measurement is in principle easy to implement with electrical isolation, but can only be implemented at high cost. The inexpensive and simple measurement by the measurement of a voltage at a resistor arranged in the current path of the battery with a known resistance value (shunt principle), on the other hand, can be implemented at low cost, but would require an additional isolator module.
Where reference is made to a battery in the context of the disclosure, this can also be intended to mean a battery cell string of a battery with a plurality of battery cell strings connected in parallel.